2001 Volume 34 Issue 1 Pages 55-65
Parallel transport of acetic acid and lactic acid by the solid-phase, and macropore diffusion within a highly porous polyaminated chitosan bead is studied by measuring equilibrium isotherms and uptake curves. The experimental adsorption isotherms of acetic acid and lactic acid are correlated by isotherm equations considering the adsorption on four different fixed functional groups. These equations were derived by simplifying the accurate isotherm equation which we have presented elsewhere. Intraparticle effective diffusivities Deff are determined from the homogeneous Fickian diffusion model. As Deff for acetic acid is about 4 times larger than those for lactic acid, these acids can be separated by the difference of the diffusion rate. The theoretical equations for the parallel diffusion model are derived from the mass balance equation based on the macropore and solid-phase diffusion and the theoretical isotherm equation mentioned above. The solid-phase diffusivity (Ds) and macropore diffusivity (Dp) are determined using Deff. Ds and Dp are independent of the bulk concentration. This parallel diffusion model correlates the experimental uptake curve well. The solid phase diffusion is the rate controlling step in β (= the ratio of the solid-phase diffusion to macropore diffusion) ≥ 3, while the macropore diffusion is the rate controlling step in β ≤ 0.3, and parallel diffusion should be considered in 0.3 ≤ β ≤ 3.